A vehicle suspension system is known in the art, which has a compression coil spring interposed between a wheel-side member and a vehicle-body member, wherein upper and lower spring seats are provided for respectively supporting upper and lower end portions of the spring, and wherein a vehicle height adjustment device is equipped for adjusting the vehicle height by regulating a position of the spring seat.
For example, Japanese patent publication No. 3,193,914 (JP 3,193,914 B) discloses a device for adjusting a vehicle height, which comprises a lower lock nut fixedly mounted on a lower arm; an upper lock nut threadedly engaging with the lower lock nut; a shank with an outer thread extending through the lower lock nut; and a spring seat integrally formed on the shank. In such a vehicle height adjustment device, the outer thread of the shank threadedly engages with an inner thread of the lower lock nut. The spring seat vertically, moves in dependence on rotation of the shank.
Further, Japanese patent application laid-open publication No. 2000-142062 (JP 2000-142062 A) discloses a device for adjusting a vehicle height, which comprises a spring seat holder fixedly mounted on a vehicle-body member, an adjustment bolt extending through the holder and threadedly engaging with the holder, and a spring seat abutting against the tip end portion of the adjustment bolt. In a condition that the bolt extends through and threadedly engages with the holder, the bolt rotates so that displacement of the bolt is caused in an axial direction of rotation. The spring seat is pressed by or released from the tip end portion of the bolt, so that the spring seat vertically moves under guidance of the spring seat holder.
In the vehicle height adjustment device as described in JP 3,193,914 B, the spring seat is integrally mounted on the shank functioning as a vehicle height adjustment bolt and is rotated together with the shank in adjustment operation of the vehicle height. However, a resilient repulsive force of a compression coil spring, which is not rotatable, normally acts on the spring seat. Therefore, in order to smoothly rotate the spring seat without rotation of the spring, a particular fabrication is required for enabling an end portion of the spring and the spring seat to relatively rotate in their contact surfaces. Thus, a manufacturing process of such a vehicle height adjustment device requires a number of manufacturing steps or a complicated manufacturing process.
On the other hand, the vehicle height adjustment device as described in JP 2000-142062 A has the spring seat and the adjustment bolt separated from each other. A torque of the bolt is converted to a pressure in an axial direction of rotation of the bolt at a contact point between the bolt and the seat. Therefore, displacement of the spring seat can be caused in the axial direction of rotation of the bolt, without rotation of the spring seat.
However, in a case of such an arrangement, the spring seat and the bolt are structurally separated from each other, and therefore, it is necessary to provide means for guiding the spring seat in the axial direction of rotation of the bolt and stabilizing a position of the spring seat. Thus, the vehicle height adjustment device as disclosed in JP 2000-142062 A is provided with a spring seat holder in position, which threadedly engages with the bolt and guides the spring seat, in addition to the bolt and the spring seat. As a result, such a type of vehicle height adjustment device requires a complicated construction of the device and a number of parts or members for the device.
An object of the present invention is to provide vehicle height adjustment device and method for a vehicle suspension system, which can restrict rotation of a spring seat associated with rotation of a vehicle height adjustment bolt and which can simplify a construction of the vehicle height adjustment mechanism, thereby reducing the number of parts or members for the device.